Good:
Weapon Speeds. A two-handed sword
is slower than a longsword or dagger, dammit!!
No half-orc Paladins. No half-orcs period, but that's a different thread.
Specialty Priests. Much better than 3e clerics, IMO.
Kits. I know some people hate 'em, but some kits are really kewl and not as ridiculous as some 3e prestige classes.
Planescape, Dark Sun & Al Qa-fricken-dim. Play 'em as they were meant to be played.
Less rules intensive than 3e. Not as condusive to rules lawyering.
No astral deva/fire giant/succubus characters.
Deities can't be killed.
Bad:
THAC0. 'nuff said.
Non-weapon proficiencies.
Level limits. Never used 'em so not really a big deal.
250,000 exp until the next level.
Dual-classing/Multi-classing: Whattya mean my human mage has to drop his mage class to pick up a level of Thief? The party's elf fighter doesn't!
Multiple attacks in a round. 2/1? 3/2, 5/2?
Less rules intensive than 3e. More subjective than third edition.
Static attributes. Once a 15, always a 15, barring some real powerful magic.